Method of producing low-dust pigment compositions

ABSTRACT

The present invention relates to a method of producing a low-dust pigment composition, which comprises suspending a filter cake obtained from preparation of the pigment, or a solid pigment, in water, adding thereto from 0.1 to 6.0% by weight, based On the weight of the pigment composition, of an amphoteric surfactant and, where appropriate, further adjuvants, and then drying the aqueous suspension to form granules, to the pigment composition obtainable according to that method, and to the use thereof in the production of colored plastics or colored polymeric particles.

The present invention relates to a method of producing stable, low-dustpigment compositions.

A method of producing low-dust colorant granules that are readilysoluble in plastics is known from EP-A-0 488 933, in which method asuspension of the colorant, which contains from 0.1 to 5.0% by weight ofa polyglycol, is dried to form granules.

U.S. Pat. No. 2,834,773 discloses a solid composition of a specificwater-soluble azo dye that comprises an addition of sequesteringcompounds, e.g. ethylenediaminetetraacetic acid.

There is a need for a method by which it is possible to obtain dust-freeor low-dust pigment compositions that also are readily pourable andresistant to rubbing and that meet current requirements, especially inrespect of ecological considerations.

It has now, surprisingly, been found that the method according to theinvention substantially satisfies the criteria set out above.

The present invention accordingly relates to a method of producing alow-dust pigment composition that comprises suspending a filter cakeobtained from preparation of the pigment, or a solid pigment, in water,adding thereto from 0.1 to 6.0% by weight, based on the weight of thepigment composition, of an amphoteric surfactant and, where appropriate,further adjuvants, and then drying the aqueous suspension to formgranules.

The pigments suitable for the method according to the invention are, forexample, those described under “pigments” in the Colour Index, 3rdEdition (3rd Revision 1987 including Additions and Amendments to No.85).

In the method according to the invention, preference is given to organicpigments from the class of the azo, azomethine, indigoid, dioxazine,quinacridone, phthalocyanine, isoindolinone, perylene, perinone, metalcomplex, alkali blue and diketopyrrolopyrrole pigments.

In the method according to the invention, special preference is given toorganic metal complex pigments of the azo, azomethine and phthalocyanineclass.

In the method according to the invention, very special preference isgiven to the organic metal complex pigments of formulae

In the method according to the invention, very special preference isgiven likewise to organic metal complex pigments, such as the manganesesalt of C.I. Pigment Red 48:4, the calcium salt of C.I. Pigment Red57:1, the barium salt of C.I. Pigment Red 53:1, the chromium complexesof C.I. Solvent Yellow 88, C.I. Solvent Orange 99, C.I. Solvent Brown42, C.I. Solvent Brown 43, C.I. Solvent Brown 44, C.I. Solvent Red 130,C.I. Solvent Red 233, C.I. Solvent Red 122, C.I. Solvent Red 127, C.I.Solvent Black 28, C.I. Solvent Black 29, and the cobalt complexes ofC.I. Solvent Yellow 89, C.I. Solvent Yellow 25, C.I. Solvent Orange 11and C.I. Solvent Red 125.

The metal complex pigments of formulae (1) to (5) are known and can beprepared according to methods known per se.

The amphoteric surfactants used in the method according to the inventionare to be understood, for example, as organic compounds that contain aradical of formula

in their molecule and are termed ampholytes, betaines or sulfobetaines.

Among such compounds there may be mentioned, for example,diethylene-triamino-penta-acetic acid, nitrilo-triacetic acid,N-hydroxyethyl-diamino-triacetic acid,1,3-diamino-2-propanol-tetraacetic acid, in free acid form or in theform of, preferably, their sodium salts, and also the compounds offormulae (CH₃)₃N⁺CH₂COO⁻ or (NaOOC—CH₃)₂N[(CHCH₃)COONa).

Special preference is given to the compound of formula

which is used in free acid form or, preferably, in the form of a salt.Salts of the compound of formula (6) that come into consideration areespecially the tetrasodium and calcium-disodium salt.

Special preference is given likewise to the compound of formula

which is used in free acid form or, preferably, in the form of a salt. Asalt of the compound of formula (7) that comes into consideration isespecially the trisodium salt.

In the method according to the invention, preference is given to the useof from 0.3 to 4.0% by weight, especially from 0.5 to 3.5% by weight, ofan amphoteric surfactant based on the weight of the pigment composition.

The granulation of the aqueous suspension comprising a pigment and from0.1 to 6.0% by weight, based on the weight of the pigment composition,of an amphotetic surfactant, and also, where appropriate, furtheradjuvants, is carried out preferably with spray-drying or fluidised-bedgranulation.

In a preferred embodiment, the aqueous suspension comprising a pigmentand from 0.1 to 6.0% by weight, based on the weight of the pigmentcomposition, of an amphoteric surfactant, is homogenised, for example ina rotor/stator mill and/or bead mill, to form a dispersion having aparticle size of from 1 to 100 μm. The resulting dispersion is thenspray-dried in a spray-dryer, preferably a pressurised nozzle tower, toform microgranules.

The present invention relates also to a pigment composition comprisingat least one pigment and from 0.1 to 6.0% by weight, based on the weightof the pigment composition, of an amphoteric surfactant, and also, whereappropriate, further adjuvants. Preferably, the pigment compositionaccording to the invention contains from 94.0 to 99.9% by weight of apigment and from 0.1 to 6.0% by weight of an amphoteric surfactant,based on the weight of the pigment composition.

With respect to the pigments and amphoteric surfactants present in thepigment compositions according to the invention, the definitions andpreferred meanings mentioned hereinabove for the method of producing alow-dust pigment composition apply.

The pigment compositions according to the invention are used preferablyfor coloring polymeric particles or thermoplastic plastics, especiallyin the form of fibres, granules or mouldings.

Preferred polymeric particles or thermoplastic plastics that can becolored in accordance with the invention are, as high molecular weightorganic materials, very generally polymers having a dielectric constant≧2.5, especially polyester, polycarbonate (PC), polystyrene (PS),poly-methyl methacrylate (PMMA), polyamide, polyethylene, polypropylene,styrene/acrylonitrile (SAN) or acrylonitrile/butadiene/styrene (ABS).

Polyester, PC and ABS are especially preferred. More especiallypreferred are linear aromatic polyesters, which can be obtained bypolycondensation of terephthalic acid or naphthalene-2,6-dicarboxylicacid and glycols, especially ethylene glycol, or condensation productsof terephthalic acid and 1,4-bis(hydroxymethyl)cyclohexane, for examplepolyethylene terephthalate (PET),polyethylenenaphthalene-2,6-dicarboxylate (PEN) or polybutyleneterephthalate (PBTP); also polycarbonates, e.g. those fromα,α-dimethyl-4,4-dihydroxy-diphenylmethane and phosgene, or polymersbased on polyvinyl chloride and also on polyamide, for example polyamide6 or polyamide 6,6.

The coloring of the high molecular weight organic materials usingpigment compositions according to the invention is carried out, forexample, by using rolling mills, mixing apparatus or grinding apparatusto admix such a pigment composition with the substrates, the pigmentcomposition being finely distributed or, where possible, dissolved inthe high molecular weight material. The high molecular weight organicmaterial with the admixed pigment composition is then processedaccording to methods known per se, such as, for example, calendering,compression moulding, extrusion, coating, spinning, pouring or injectionmoulding, as a result of which the colored material acquires its finalshape. Admixture of the pigment composition according to the inventioncan also be effected directly before the actual processing step, forexample by continuously metering, directly into the inlet zone of anextruder, the pigment composition and a granulated or pulverulent highmolecular weight organic material and, where appropriate, also otheringredients, such as additives, the constituents being mixed in justbefore being processed. Generally, however, preference is given tomixing the pigment composition according to the invention into the highmolecular weight organic material beforehand, since more uniformlycolored substrates can be obtained.

In order to produce non-rigid mouldings or to reduce brittleness, it isfrequently desirable to incorporate so-called plasticisers into the highmolecular weight compounds prior to shaping. There may be used asplasticisers, for example, esters of phosphoric acid, phthalic acid orsebacic acid. In the method according to the invention, the plasticiserscan be incorporated into the polymers before or after the incorporationof the colorant. It is furthermore possible, where appropriate, also toadd further ingredients, e.g. fillers or siccatives.

In order to improve light fastness properties, UV absorbers areadvantageously admixed with the plastics or polymeric particles to becolored by the compositions according to the invention.

The present invention relates also to the above-mentioned use of thecomposition according to the invention.

The following Examples serve to illustrate the invention. Unlessspecified otherwise, the parts are parts by weight and the percentagesare percentages by weight. The temperatures are given in degreesCelsius. The relationship between parts by weight and parts by volume isthe same as between grams and cubic centimetres.

EXAMPLE 1

In an apparatus equipped with a stirrer, 200.0 parts by weight of anaqueous colorant filter cake containing 97.5 parts by weight of themetal complex pigment of formula

are homogeneously mixed at room temperature, with vigorous stirring,with 1.6 parts by weight of the compound of formula

and 382.4 parts by weight of water, and then ground in a Fryma mill.

Using a NIRO pilot plant scale atomizer having a binary nozzle, thehomogeneous suspension is then spray-dried at an inlet temperature of150° C., an outlet temperature of from 105 to 110° C. and a watervaporization capacity of 1 kg/h.

Low-dust, free-flowing microgranules having an average particle size offrom 5 to 15 μm and a residual water content of about 2% by weight areobtained.

EXAMPLE 2

In an apparatus equipped with a stirrer, 200.0 parts by weight of anaqueous colorant filter cake containing 97.5 parts by weight of themetal complex pigment of formula (1) are homogeneously mixed at roomtemperature, with vigorous stirring, with 1.6 parts by weight of thecompound of formula

and 382.4 parts by weight of water, and then ground in a Fryma mill.

Using a NIRO pilot plant scale atomizer having a binary nozzle, thehomogeneous suspension is then spray-dried at an inlet temperature of150° C., an outlet temperature of from 105 to 110° C. and a watervaporization capacity of 1 kg/h.

Low-dust, free-flowing microgranules having an average particle size offrom 5 to 15 μm and a residual water content of about 2% by weight areobtained.

1. A method of producing a low-dust pigment composition, which comprisessuspending a filter cake obtained from preparation of a pigment, or asolid pigment, in water, adding thereto from 0.1 to 6.0% by weight,based on the weight of the pigment composition, of an amphotericsurfactant selected from the group consisting of ampholytes, betainesand sulfobetaines that contain in their molecule a radical of formula

and optionally further adjuvants, and then drying the aqueous suspensionto form granules.
 2. A method according to claim 1, wherein the pigmentis a suspension of an organic metal complex pigment.
 3. A methodaccording to claim 2, wherein the organic metal complex pigment isselected from the group consisting of


4. A method according to claim 1, wherein the amphoteric surfactant isformula (6)

wherein (6) is the free acid form or a salt thereof.
 5. A methodaccording to claim 1, wherein the amphoteric surfactant is formula (7)

wherein (7) is the free acid form or a salt thereof.
 6. A methodaccording to claim 2, wherein the amphoteric surfactant is formula (6)

wherein (6) is the free acid form or a salt thereof.
 7. A methodaccording to claim 2, wherein the amphoteric surfactant is formula (7)

wherein (7) is the free acid form or a salt thereof.
 8. A methodaccording to claim 3, wherein the amphoteric surfactant is formula (6)

wherein (6) is the free acid form or a salt thereof.
 9. A methodaccording to claim 3, wherein the amphoteric surfactant is formula (7)

wherein (7) is the free acid form or a salt thereof.
 10. A low-dustpigment composition comprising at least one organic metal complexpigment of the azo, azomethine or phihalocyanine class and from 0.1 to6.0% by weight. based on the weight of the pigment composition, of anamphoteric surfactant selected from the group consisting ofdiethylene-triamino-pentaacetic acid, nitrilo-triacetic acid,N-hydroxyethyl-diamino-triacetic acid,1,3-diamino-2-propanol-tetraacetic acid, in free acid form or in theform of their sodium salts, a compound of formula (CH₃)₃N⁺CH₂COO⁻, acompound of formula (NaOOC—CH₃)₂N[(CHCH₃)COONa), a compound of formula

which is used in free acid form or in the form of a salt and a compoundof formula

which is used in free acid form or in the form of a salt.
 11. A methodof producing colored plastics or colored polymeric particles, whichcomprises admixing a pigment composition according to claim 10 with saidplastics or polymeric particles.
 12. A composition according to claim 6comprising a metal complex pigment of formula (1)

and from 0.1 to 6.0% by weight, based on the pigment composition, of anamphoteric surfactant of formula (7).